The 4th Australasian Ground Control in Mining Conference (AusRock) conference will take place in Sydney 28-30 November and is hosted by the AusIMM. The conference will provide a vehicle for information exchange between thecoal and metalliferous sectors of the industry with a focus on new technologies and developments, industry needs and mine site problem solving, and practical case studies. AMC Consultants expert in geotechnical engineering, Adrian Penney, looks forward to sharing his knowledge and expertise by presenting the papers, Proneness of competent over-stressed intact rock to violent fracturing and Raise bore stability and risk assessment empirical database update.
Proneness of competent over-stressed intact rock to violent fracturing
11:50 AM – 12:10 PM
Friday, November 30, 2018
M.F. Lee, A.R. Penney, B.L. Saisnbury
For most practical rock engineering purposes, stress versus strength conditions around underground openings for which rock masses fail and their various modes of failure, are reasonably well-understood and predictable. Some rock masses and particular rock types fail slowly and relatively quietly. However, others can fail rapidly, violently and maybe with the ejection of significant broken rock.
In some countries and in some mines, the latter style of violent fracturing and failure of the rock mass is referred to as ‘strain bursting’. It can be alarming and extremely hazardous to nearby miners and machines. For such situations, the design and installation of appropriate ground support, to provide a safe work place, can be challenging.
At any particular mine site, it’s often generally understood which local rock masses (rock types) are prone to strain bursting. Competent and strong siliceous rocks and some massive sulphides are often the main offenders. While some neighbouring, equally-competent and strong rocks might also fail, they do so more quietly and without ejection. To understand this contrast, a better understanding of the fracturing process is required other than simple and standard strength versus stress considerations.
Suites of standard intact rock properties from numerous Australian mines have been used to define and help understand different high-stress failure styles for component intact rock; especially those prone to violent fracturing (strain bursting). Simple considerations of micro-fracturing (defects in the intact material), plus the available energy at failure versus the energy consumed during fracturing, distinguishes between over-stressed and competent rock types that fracture violently and those that don’t.
Raise bore stability and risk assessment empirical database update
2:30 PM – 2:50 PM
Friday, November 30, 2018
A.R. Penney, R.M. Stephenson, M.J. Pascoe
The empirical McCracken and Stacey stability and risk assessment method has been in use for more than 20 years to assess geotechnical stability issues for raise bored shafts. The methodology has been applied with various levels of success. Increasingly, trends in mining and civil tunnelling have been towards larger diameter, single pass, raise bored shafts to rapidly provide means of ventilation, material movement (ore passes), or emergency egress. Identifying and assessing potentially problematic zones before raise boring commences can allow for appropriate risk-based decisions on construction, or to investigate alternative solutions. The implementation of a proactive solution to raising through an identified weak zone is preferred to the application of an engineered solution to an area subjected to substantial instability or failure. Methods for investigating potentially problematic areas are discussed in this paper based on AMC’s benchmarking data. Proactive investigation programmes resulting from these investigations are also discussed.
Previous publications discussing the benchmarking data have concentrated on Australian case studies. Increased efforts and recent updates have been made to expand the database to include international case studies. This has provided further refinement of lower bound ‘raise bore rock quality index’ (QR) values, and various rock mass parameters for stability assessments.
Adrian Penney MAusIMM CP(Geotech), RPEQ
Technical Services Manager / Principal Geotechnical Engineer
Adrian is a geotechnical engineer with more than 20 years’ experience in mining. Since graduating in 1997, Adrian has held both operational and consulting roles over his career. He is the Technical Services Manager at AMC’s office in Melbourne, with a specialty in underground metalliferous rock engineering. His main areas of expertise are in ground support selection, seismic data analysis, field investigations, geotechnical and mining studies, incident investigations, and incident investigations. Adrian is currently the Chair of the AusIMM Melbourne Branch, and is the Vice Chair and Geotechnical representative of the AusIMM Chartered Professional Program. In his spare time, Adrian enjoys spending time with his family, normally running his kids to various sporting interests.